1. Field of the Invention
This invention relates to a method and apparatus applicable inter alia to determining catalyst operation in automotive vehicle exhaust systems and applicable to comparable operations for other internal combustion engine systems. A principal application of the invention is to a method and apparatus for use in routine testing of automotive vehicle exhaust gas emissions. In such testing work, the presence of catalytic systems, and the operation of such systems has a direct bearing on the results obtained from such testing work, and there is a need for a more systematic approach to dealing with the variables introduced into such testing work by the presence of catalytic converters.
A broader aspect of the invention relates to the analysis of exhaust gases from an engine system in such a way that transient changes in the concentrations of the exhaust gases are used to provide an indication of the state of operation of the engine and/or its exhaust delivery system including a catalytic converter, if provided.
In automotive applications of the present invention, it will be understood that the method and apparatus will usually find application as part of the routine test equipment employed for analyzing the exhaust gas emissions from such automotive vehicles. The information provided by the method and apparatus of the invention in relation to the operation of a catalytic converter system will usually be used as part of the systematic test work carried out to determine the levels of exhaust gas emissions, and in particular as to whether such emissions meet legislative requirements. The information provided by the method and apparatus of the invention enables a test operation to be carried out with greater certainty and precision. It also enables, in certain cases, a relatively rapid determination to be made that replacement of a catalytic system is required or that associated control equipment such as the so-called lambda sensor or the vehicle's ECU require attention.
2. Description of the Prior Art
Turning to the general background of the invention, it is well known that in response to legislative pressure, catalytic converters are being installed in all new vehicles, at least in certain countries. A catalytic converter however may fail or degrade as a result of age or prolonged usage. Damage arising from failure of another component within the emissions system of the vehicle can also occur. Examples of such related failures are failures of the so-called lambda sensor (which senses the appropriate air/fuel ratio in the engine fuel feed and controls same to ensure proper operation of the catalyst). Another example is the engine electronic control unit (ECU), operation of the engine with leaded fuel or with too lean a fuel mixture, physical shock etc. These factors can all cause total or partial failure of a catalytic converter. Additionally, such converters do not operate at low temperatures i.e., during the first minutes of operation of a vehicle, and neither do they operate in conditions of low exhaust gas flow, e.g., when the engine is idling in heavy traffic.
Accordingly, tests carried out to determine whether a vehicle's exhaust emissions meet legislative requirements need to take into account the state of functionality of the catalytic converter itself and/or its associated control equipment. If, for example, a catalyst fails to turn on (known as "light-off") during emissions testing, as a result of the vehicle not having been warmed up or operated for a sufficient length of time, the vehicle may fail its roadworthiness test. Equally, a catalyst may turn off during testing if the vehicle idles (e.g., at 1K rpm) too long between test phases (e.g., at 2K rpm). A means for automatically indicating catalyst switch-on and/or switch-off would greatly assist in avoiding this problem. Furthermore, a means to detect related partial or complete failures such as those of associated control equipment and an ability to detect and distinguish between such failures and partial or complete failure of the catalyst itself would be an aid to more general diagnostic work.
There is disclosed in U.S. Pat. No. 5,175,997 (Blanke) a feedback control system which analyses three different constituents of the exhaust stream and selectively controls the fuel mixture and air injection of the engine to positively activate and deactivate the catalytic converter, for taking measurements from which the efficiency of the converter can be calculated. The system does not use the gas concentration data to determine the operating state of the converter.
U.S. Pat. No. 5,341,643 (Hamburg) discloses an on-board feedback control system which utilises analysis of plural constituents of the exhaust emissions to control the air/fuel mixture operation of the engine so as to maintain optimum convertor efficiency.
U.S. Pat. Nos. 5,157,921 (Ito) and 5,400,592 (Mukaihira) and 5,417,061 (Maeda) and 5,526,643 (Mukaihira) all disclose on-board systems for detecting deterioration of the catalyst of a catalytic convertor system by means of monitoring concentrations of one or more constituents of the exhaust emissions.
To the best of the Applicants' knowledge a method and apparatus for determining the characteristic shape of the plots of gas concentrations against time of two or more constituents of the gas content of the exhaust output from an internal combustion engine as a means for determining catalyst state of operation, such as catalyst-on or catalyst-off condition, or indeed the analysis of the switch-on and switch-off speeds as a basis for determination of catalyst efficiency and/or remaining life, has not previously been proposed.